The present invention relates to an eraser, and more particularly concerns an eraser which can be used with a light touch is less susceptible to cracking, is superior in its scrap-collecting property, and has an excellent erasing property.
An eraser (rubber eraser) for erasing handwriting written with a writing tool such as a pencil is composed of an elastic material of an eraser composition comprising rubber components or resin components such as rubbers, plastics and thermoplastic elastomers, and additive agents such as fillers and polishing materials.
In general, with respect to the performance required for an eraser, the erasing property and touch in use are listed; however, in recent years, the form of eraser scraps and its scrap-collecting property (combining property for eraser scraps) have become important factors. These properties mainly are determined by the hardness of the elastic material of an eraser composition constituting an eraser main body. In general, the softer the elastic material, the better the erasing property and the better the scrap-collecting property; in contrast, as the elastic material becomes softer, the touch in use becomes heavier, and it is susceptible to cracking due to repeated use and use with a high pressure. The hardness of the eraser main body can be controlled by adjusting factors such as the type, viscosity and molecular weight of rubber components and resin components, the type and compounded ratio of plasticizers and softeners and the type and compounded ratio of additive agents, such as polishing agents, etc., as well as adjusting manufacturing conditions. Thus, taking the above-mentioned trends into consideration, the manufacturers determine the hardness of an eraser by adjusting the composition and manufacturing conditions. Therefore, in the conventional erasers, it has not been possible to achieve the best states in all the properties including the erasing property, eraser-scrap-collecting property, touch in use, crack resistant property (rupture resistant property), etc., and the specifications are determined by taking into account the balance of those properties so as not to raise any problem in practical use.
Here, Japanese Unexamined Patent Publication No. 8-258493 proposes an eraser material composed of an eraser base material including a vinylchloride resin, a plasticizer and a filler, and a self-abrasion-type porous material. In accordance with this invention, it is possible to improve the strength without impairing the erasing property, and to provide an eraser with high toughness.
However, Japanese Unexamined Patent Publication No. 8-258493 defines that the self-abrasion-type porous material is a composite material consisting of layers made of binder layers that are continuous layers having a structure like a pencil core material and discontinuous layers composed of an inorganic constituent material, such as boron nitride, talc and mica, that does not contribute to adhesion to the interfaces. Therefore, this invention has a mechanism in which the inorganic constituent material, such as boron nitride, talc, and mica, combined by the binder is allowed to finely crumble like a pencil core due to friction, etc. against paper, and erases handwritings on the paper in combination with the eraser base material.
Therefore, since the eraser of Japanese Unexamined Patent Publication No. 8-258493 uses the porous material containing the inorganic constituent material, it has an extreme reduction in the elasticity as compared with conventional erasers, although it has improved strength as compared with conventional erasers; thus, the reduced elasticity impairs the erasing property that inherently should be exerted by the erasing base material. Moreover, the extreme reduction in the elasticity causes an unusual touch as compared with conventional erasers, failing to provide a good touch in use. Moreover, it is necessary for the eraser not only to be less susceptible to cracking at the time of erasing handwritings, but also to generate continuous eraser scraps in a collected manner after erasing; however, since the inorganic material different from the rubber base material is used as the porous material, it is difficult to generate sufficiently collected eraser scraps.